Final drives are utilized in a variety of motorized machines, including automobiles, buses and trucks, as well as off-road machines including those involved in construction, mining, and agriculture. The final drives of many off-road machines incorporate gear ratio reductions between their input and output shafts. Such gear reductions have been commonly achieved by either planetary gear sets or a combination of spur and planetary gear sets. One type involving the combination is described in U.S. Pat. No. 5,147,255 granted to Strehler et al., which is incorporated by reference herein.
Strehler et al. features a double reduction gearbox that incorporates a wet brake system sandwiched between respective spur and planetary gear sets to minimize physical space requirements for brakes of an industrial truck. According to Strehler et al., prior to Strehler et al. brakes were physically contained within structures situated only outside of the drive axle gearbox. As such, Strehler et al. introduces the placement of a wet brake inside of a drive axle gearbox.
Disadvantages of Strehler et al. include spatial limitations with respect to the amount of braking surface that can be contained within the Strehler gearbox, as well as limitations on potential physical locations of actual brake structures within Strehler's gearbox. Ideally, a gearbox could be manufactured that contained additional interior space for accommodating increased braking surface, albeit without commensurate requirement of employing a larger gearbox.
Finally, a major challenge associated with design and construction of gearboxes has been a continuing pressure to achieve more performance and functionality, while using fewer parts in smaller spaces with less weight. Among other things, this has translated into a quest for reducing numbers of gearbox parts, including actual numbers of gears employed, while squeezing additional structures, such as brakes and/or larger brake surfaces, into the gearbox housing envelope. As such, it would be desirable to be able to manufacture a double reduction gearbox possessing substantially fewer gears, while being able to offer greater braking capacity within the housings of gearboxes, albeit without increasing the size of the gearbox housing.